O. A. Ponomarev

Ziegler-Natta catalysts and the reactive centres composition during the stereospecific polymerization of α-olefins

The chemisorption of (CH3)2AlCl on the crystal surfaces of the α- and β-modifications of TiCl3 have been calculated by the “atom-atom” potentials method. The reactive centres were found to have the same composition for 80% α-TiCl3 and 30% β-TiCl3; their amounts diminished when the temperature was raised. These results agree with those given in the literature about the yields of stereospecific α-olefin polymers over the catalytic systems containing the α- and β-forms of TiCl3.

On the nature of the activity of the systems C2H5AlCl2-alcohol in the cationic polymerization of olefins☆

A study has been made of some physico-chemical properties and of the activity of the systems C2H5AlCl2-alcohol in isobutylene polymerization (transformation of isobutylene models). A quantum chemical calculation has been carried out for some models of active centres in these systems. The calculated data agree with the experimental results, which points to the carbocationic activity of alcohol.

The nature of the active centres in Ziegler-Natta catalyst systems☆

Abstract The results of quantum chemical analysis show that a propagation reaction in which an Al … R … Ti group partakes is preferable to one involving a TiR group. The active role played by the,organoaluminium component is exhibited in smoothing ont ground state energy changes, while simultaneously facilitating the stabilization of monomer in the form of a polymer unit.

Quantum-chemical calculation of reactive fuels as H-acids

Abstract The theoretical evaluation of acid strength reactive fuels, through quantum-chemical calculation by the method CNDO/2 of the charges on hydrogen atoms, which correlate with the universal index of acidity is presented. Correlations defining relationship of some parameters of combustion with the accounting parameters of acidic strength of the fuels are established to oxygen.

Effect of Electronic Charge on Oxygen Atom of Oxygen-Containing Oxidizers on Characteristics of Reactive Rocket Fuels

Abstract The calculations of typical oxygen-containing oxidizers of rocket fuels OF2, O2, ClO3F, H2O2, N2O 4, HNO3, were carried out by quantum chemical semi-empirical MNDO method in Dewar and Teel parameterization with minimization of total energy of molecular system by Davidon-Fletcher-Powell method. The optimized electronic and geometric structure of these oxidizers was obtained. We established correlative dependencies between some parameters of the following reactive fuels (H2, N2H4, N2 H2(cH3)2 ∼CH2∼, Al H3, B5H9, Be H2): and minimum electronic charge on oxygen atom qomin of oxygencontaining oxidizers. The latter being calculated by the MNDO method.

Theoretical Estimation of Acid Strength of Fluorine Hydrogen-Boron Fluoride Complexes

Abstract The calculation of complexes R n BF3-n . HF (there is R = CH3 and C2H5) has been carried out by the quantum-chemical semi-empirical MNDO method in Dewar and Teel parameterization. The geometrical and electronic structure of these complexes was obtained. On an example of simple H-acids we estimated their acid strength. We found that irrespective of the ligand surrounding of B atom the complexes R n BF3-n HF have rather high acid strength (pK a = 17.9 14.9).

Quantum-chemical calculation of active centers in aquo complexes of aluminum chlorides

Since the hydrolysis of R AICI by water in the presence of electron-donor compounds n 3-n is accompanied by the evolution of HC! (an acid that is stronger than water), we cannot deny the cocatalytic effect of HCI, which may be manifested through the formation of ternary complexes (see direction B in the reaction scheme). In this case, different versions of the AC structures are possible, differing, for example, in the nature of the aluminum component.

The type of reactive centres present in the alkylaluminium aquo-complex used in the electrophilic polymerization of olefins☆

Calculation and experimental results (the physical and chemical properties, and the activity in the isobutylene polymerization) concerning the nature of the reactive centres of aquo-complexes C2H5AlCl2·H2O are described. These compounds are shown to digress from the analogous complexes with HCl and not to be an H acid, but are characterized by a low Lewis acidity. An initiation of the isobutylene polymerization over C2H5AlCl2·H2O presumes a prior C2H5AlCl2 reaction with H2O in the presence of the monomer and the formation of an alumoxane aquo-complex as the actual initiator. The transformation of the alkylaluminium dichloride aquo-complex to that of alumoxane has been proved by direct methods (IR spectroscopy, the use of isobutylene models, C2H5AlCl2·D2O), as well as by analyses of the dependences of the isobutylene (IB) polymerization (the polymer yield and the initial process rates as a function of the H2O content of the aquo-complex); an initiation scheme of the IB polymerization by the alumoxane aquo-complex which is characterized by a sufficiently large strength of the acid centres (H0 ⩽ − 8) is suggested. In contrast with the AlCl3 complexes, C2H5AlCl2·H2O is highly selective in the IB polymerization when the latter is present in a mixture with other olefines; the selectivity drops rapidly on changing from an inert solvent (hexane) to a polar (CH2Cl2). It is concluded that the C2H5AlCl·H2O complexes forming in the absence of IB differ in type of reactive centres from those forming in situ and those based on AlCl3.